1. Field of the Invention
The present invention relates generally to an improved reverse buckling rupture disk apparatus, and more particularly, but not by way of limitation, to a reverse buckling rupture disk assembly including a reverse buckling rupture disk, at least one annular support member and knife means for severing the rupture disk upon the reversal thereof.
2. Description of the Prior Art
Reverse buckling rupture disk apparatus including a reverse buckling rupture disk, at least one annular support member for supporting the rupture disk in a pressure relief area and knife means for severing the rupture disk upon the reversal thereof have been developed and used heretofore. For example, see U.S. Pat. No. 3,294,277 issued Dec. 27, 1966.
A variety of knife means have been utilized in such reverse buckling rupture disk assemblies. The most common such knife means have been comprised of three or more blade legs having sharpened cutting edges formed thereon attached together at the internal ends and attached to the support member at the external ends thereof. Upon reversal of the rupture disk, the reversing portion thereof contacts the blade legs and is severed whereby full opening of the rupture disk occurs. Most of the prior knife means of the type described above have included four blade legs attached together at the internal ends at right angles to each other and attached at the external ends to the rupture disk support member.
In substantially all of such heretofore used knife means, the cutting edges formed on the blade legs are positioned either in a single plane which is parallel to the plane of the peripheral portion of the rupture disk and the support member seating surface therefor, or the cutting edges of the blade legs are inclined towards the rupture disk from the external ends to the internal ends thereof. Such cutting edge configurations generally bring about the severing of the rupture disk from the center of the reversing portion of the rupture disk outwardly. That is, the reversing portion of the rupture disk is first cut by the cutting edges of the blade legs at the center thereof and the cutting process proceeds progressively outwardly from the center to the periphery of the reversed portion. This cutting process or mode sometimes results in the reversal of the rupture disk without the rupture disk being severed because the reversal of a reverse buckling rupture disk begins at the side or transition connection area and progresses inwardly. That is, when a reverse buckling rupture disk reverses prematurely, i.e., at a fluid pressure level lower than the predetermined design rupture pressure thereof, due to damage to the disk during handling or installation or other similar cause, the reversal takes place from a side of the reversing portion inwardly and can take place slowly or only partial reversal can result whereby the central portion of the rupture disk does not contact the heretofore used knife means with enough force to sever the rupture disk. When reversal without severing takes place, a dangerous overpressure condition in the vessel or system being protected can result before the rupture disk ruptures.
As is well understood by those skilled in the art, it is generally necessary for a reverse buckling rupture disk assembly to be designed such that if premature reversal takes place without the disk being severed by the knife means, the reversed disk ultimately ruptures at a pressure level no more than 1.5 times the predetermined design rupture pressure. The reason for this is that the predetermined design rupture pressure is usually at a level equal to or near the working pressure of a vessel or system being protected and such vessel or system can withstand and is tested to a maximum pressure of 1.5 times the working pressure. If a reverse buckling rupture disk prematurely reverses and is not severed by the knife means, in some applications a pressure level exceeding 1.5 times the predetermined design rupture pressure of the disk must be exerted on the disk to bring about the severance thereof. Thus, heretofore, in such applications, the possibility of a dangerous overpressure condition being allowed to occur in the vessel or system being protected has existed.
By the present invention an improved reverse buckling rupture disk apparatus is provided whereby the severing of the rupture disk upon its premature reversal is insured at a pressure level no greater than 1.5 times the predetermined design rupture pressure of the disk. The term "predetermined design rupture pressure" is used herein to mean the predetermined fluid pressure differential which must be exerted on a normally functioning reverse buckling rupture disk to cause the rupture disk to reverse.